body {
    background: blue;
    font-size: 14px;
    margin: 0;
    padding: 0;
    height: 100%;
    display: flex;
    align-items: center;
    justify-content: center;
}
.app {
    width: 100%;
    height: 100%;
    display: flex;
    flex-direction: column;
}
.app-header {
    -webkit-app-region: drag;
    display: flex;
    padding: 5px 10px;
    background: #fff;
}
.app-header-right {
    -webkit-app-region: no-drag;
    margin-left: auto;
    display: flex;
    align-items: center;
}
#btn_close {
    cursor: pointer;
}
.app-body {
    padding: 8px 8px;
    background: #D5D5D5;
    height: 100%;
}
.app-footer {
    background: #D5D5D5;
    padding: 8px 8px;
    text-align: center;
}